Method of making a tobacco smoke filter



June 19, 1962 H. B. PARMELE METHOD OF MAKING A TOBACCO SMOKE FILTERFiled July 13, 1953 United States Patent Cfifice 3,039,908 Patented June19, 1962 3,039,908 METHOD OF MAKING A TOBACCO SMOKE FILTER Harris B.Parmele, Glen Ridge, NJ., assignor to Hollingsworth & Vose Company, acorporation of Massachusetts, and P. Lorillard Company, a corporation ofNew Jersey, jointly Filed July 13, 1953, Ser. No. 367,499 5 Claims. (Cl.156200) This invention relates to tobacco smoke filters and to methodsof making the same.

It has been determined that particle sizes in tobacco smoke range fromabout 0.1 to 1.0 micron in diameter, Varying according to the smokingconditions, such as draft, heat, nature of tobacco, and the like.However, those particles which impart flavor and aroma, i.e., thosewhich give the smoker satisfaction, are relatively small in size, beingon the order of about 0.1 to about 0.4 micron in diameter, exist in fargreater proportion in the smoke than do the larger particles which havediameters from about 0.4 to about 1.0 micron. Although the volumetricratio of smaller particles is about 60% to 80% to about 20% to 40% ofthe larger particles, the numerical ratio is upwards of ten to one.

I have found that the larger particles are principally responsible forthe color of the smoke, since they are largely composed of the tarrysubstance in tobacco smoke. It has been demonstrated that when thequantity of these larger particles in the smoke is reduced, smokers whoare ordinarily sensitive to the toxic effects of smoking become lesssensitive without noticeable impairment of the satisfaction which theyderive from smoking. I have observed that exhaled smoke is substantiallydevoid of these larger particles which apparently lodge in the mucoussurfaces of the nose, throat and lungs, together with some of thesmaller particles, and are subsequently absorbed along with them, butdoubtless at a slower and hence more harmful rate, thereby cumulativelyaggravating toxic efiFects.

It is accordingly the object of this invention to provide a tobaccosmoke filter and method of making the same which selectively removes theaforementioned larger particles from the smoke taken into the mouth ofsmoker.

In a preferred embodiment of the selective tobacco smoke filter of thisinvention, textile fibers of substantially uniform diameter, but ofrandom length, are arranged heterogeneously in a semi-felted cylindricalmass affording a labyrinth of extremely fine but highly tortuouspassages through which the smoke is drawn and in which its direction issharply changed countless times in such a way that the larger particlesare selectively thrown out of the smoke stream to become trapped in thepassages, thereby leaving the smaller tasteand aroma-producing particlesin the smoke passing into the mouth of the smoker. Preferably, thefibers are stiffened and are bound together in the aforementionedheterogeneous arrangement by a suitable inert binder, so that the filteris rendered sufiiciently firm and resilient not to be readily compressedbetween the smokers lips to such a degree that freedom of draw andconsequent flow of smoke is materially impaired.

A preferred method of making the selective tobacco smoke filteraccording to this invention comprises semifelting the random lengths offiber in a loose web, gathering the same into a roving having a diameterseveral times that of the finished filter, compressing the rovingradially, i.e., contracting it circumferentially into a rope having afraction of the diameter of the roving to thereby reduce the macro-voidstherein to micro-voids, wrapping the rope in a tubular paper wrapper,and severing the wrapped rope into units or plugs of the desired lengthfor incorporation in a cigarette or other smokers article. Prior togathering the semi-felted web of fibers into the roving, or during theroving formation, a thermo-responsive binding material is mixed orotherwise incorporated in or applied to the fibers and thereafter theroving is heated to a sufiicient degree to activate the binder and causeit to hold the fibers in the aforementioned heterogeneous relation andto impart firmness and resiliency thereto. Preferably, but notnecessary, the activation of the thermo-responsive binder is eifectedafter the roving has been compressed into the reduced-diameter rope, butprior to severing the same.

it will be seen that the tobacco smoke filter of this invention and themethod of making the same according to this invention provide aneflicient and highly selective means for removing the largertoxicity-aggravating particles without noticeably impairing thesatisfaction which the smoker derives from the tobacco.

For a more complete understanding of the invention, reference may be hadto the accompanying drawings, in which:

FIGURE 1 is a schematic diagram of the apparatus for making the filteraccording to the method of this invention, and illustrates thesuccessive steps of forming the roving, radially compressing it into areduced-diameter rope, wrapping it in paper, heat-activating thethermoresponsive binder, cooling the rope to set the binder, andsevering the rope into finished filter units or plugs;

FIG. 2 is an enlarged perspective view of one of the filter unitsembodying the invention and made according to the method of thisinvention, the tubular paper cover being shown partially unwrapped toexpose the filter portion and to generally indicate its construction;

FIG. 3 represents a microscopic view of a portion of the filter of FIG.2, and illustrates the random, heterogeneous arrangement of the fibersand the binder holding them in that arrangement by securing contactingfibers together at their points of contact, and

FIG. 4 represents a larger microscopic view of a portion of the filtermade according to a modification of the resin-treating step of thefibers.

in carrying out the method or" the invention, fibers of textile grade,having diameters of about 2 to about 5 denier (about 14 to about 23microns) and of random lengths between about .03 to about 2.0 inches arestirred and mixed together so that they are highly intermingled in aheterogeneous mass with the shorter fibers lying at various anglesacross the longer fibers in a non-parallel arrangement to form a thin,loose, semi-felted web capable of being handled, but having littleself-sustaining strength. Natural fibers of vegetable origin such ascotton, or synthetic fibers, such as cellulose acetate, acetate rayon,vis cose, nylon and the like, of the aforementioned diameters andlengths, may be used alone or as mixtures of two or more of them,regardless of their nature. Where mineral fibers, such as glass orasbestos fibers or their equivalents comprise the web-or are admixedwith the textile fibers, the diameter of such mineral fiber is on theorder of 3 microns or less and in that case the labyrinthine filtrationeffect is augmented by impingement of the smoke particles on the finemineral fibers or their equivalents, in the manner described incopending application Serial No. 260,187, filed December 6, 1951, byHarold W. Knudson, now Patent No. 2,761,798, issued September 4, 1956.

The semi-felted web so formed is gathered into a roving according tousual textile practice, i.e., with the long fibers extending generallylongitudinally, the quantity of the gathered fibers being such that theroving will have a diameter several times the diameter of the ultimatefilter unit or plug. For example, if the finished diameter of the filterunit is to be, say, 0.3 inch, the free diameter of the roving would beat least twice and up to ten times larger, or between about 0.6 andabout 3 inches in free diameter.

Inasmuch as such rovings are inherently irregular in cross-sectionaldensity and non-uniform in arrangement of the fibers along the length ofthe roving, due to the manner in which the original semi-felted web isformed, it is preferred that the roving that is supplied to theplugmaking machine be made up of several relatively small diameterstrands formed in the same way from the semifelted web and then combinedinto a single roving of the said diameter for supply to the plug-makingmachine. To that end, strands of the semi-felted fibers are formed inthe manner described but of diameters such that when the predeterminednumber thereof are brought together into a single roving the latter willhave the requisite diameter.

By way of example, three reels 10, 11 and 12, each containing therespective strands 13, 14 and 15 to be combined, are illustrated in FIG.1 as journalled on a suitable frame 16 and simultaneously feeding intothe conical thimble or eye 17 where they are combined into the roving18. If the free diameter of the roving 18 is to be about one inch, thediameter of the individual strands 13, 14 and 15 from which the singleroving 18 is made will be about one-third inch. Similarly, if four suchstrands are to be combined into a one inch roving 18, the strands 13, 14and 15 would be about one-fourth inch in diameter and four correspondingreels then used.

Preferably, the three strands 13, 14 and 15 are lightly twisted tofurther improve cross-sectional uniformity by averaging out theaforementioned inherent irregularities. One convenient way to effectsuch a light twist is to slowly rotate the gathering thimble 17 aboutits axis as by a suitably driven belt 19, or the like, the interior ofthe thimble 17 being knurled or otherwise roughened to afiord asufliciently frictional surface.

The lightly twisted roving 18 is then uniformly compressed radially tothe rope 21 having the desired diameter of about 0.3 inch in thetapering cone 2% leading to the plug-making machine of the general typeshown in my Patent No. 2,793,572, issued May 28, 1957. As theredescribed, the rope 21 is wrapped in a strip of paper 22, such ascigarette paper, supplied from spool 23 to the wrapping mechanismschematically shown at 24 in FIG. 1. The seam of the relatively tubularpaper wrapper 25 is sealed at 26, and, subject to certain preferredintermediate steps, may then be severed into units 27 of about threeinches long by the flying knife mechanism indicated at 28. These units27 are cut into shorter lengths, assembled with tobacco and againsevered to form the filter of a cigarette, each filter having a lengthof about one-half inch and the diameter of the finished cigarette, whichmay be about 0.3 inch, the diameter of the rope 21 in the given example.

The purpose of the radial compression of the roving 18 from a freediameter to a fraction thereof into the rope 21 is to reduce themacro-voids therein to microvoids, so that all tortuous passagestherethrough have a minimum diameter less than the diameter of the largeparticles, i.e., those larger than 0.4 micron in diameter. However, itis not the diameter of the passages that selectively precludes passageof the larger particles, but rather, it is the highly tortuous nature ofthese passages formed between the fibers that performs that function,augmented by impingement of the smoke particles on fine fibers havingdiameters on the order of the smoke particle diameters, in cases Where asmall proportion of such fine fibers are incorporated in the filter inthe manner described in said Knudson patent. Primarily, the reduction indiameaiforded by reducing cone is to enhance the tortuous nature of thepassages, although, secondarily, no through or continuous passagesremain which have a minimum diameter capable of passing any measurablequantity of the larger particles. An incidental purpose of compressingthe roving into a rope is to hold the filter securely in its tubularwrapper 25.

The random, heterogeneous arrangement of the fibers constituting theradially compressed plug 21 is generally illustrated in FIG. 2, fromwhich it will be seen that a labyrinth of myriad highly tortuouspassages is formed through the interior of the tubular wrapper 25, asshown partially unwrapped in FIG. 2.

I have estimated that for a filter made of glass fibers of three microndiameter, a plug of about one-half inch in length and the diameter of acigarette contains approximately two miles of fiber and approximately 54/2 miles of air passages, the latter considered for comparison, ashaving average diameters of 3 microns. With this ratio of approximately2 to 54 /2 of solid fiber material to passages or voids between thefibers, it is evident that the void portion of the plug is extremelyfinely subdivided, so as to be an effective filter to remove up to thedesired physiological amount of harmful solids and yet afford asatisfactory draw and the conduction of the desirable aroma and tastecomponents of the cigarette smoke. Although a gross filtering efficiencyof 40 to 50 percent offers measurable physiological advantages to thesmoker in the filter of this invention, the larger particles are removedto a measurably greater extent, thereby greatly enhancing itsphysiological advantages. In case the filter is made of textile fibersor a mixture of them, or a mixture of them with mineral fibers, theproportion given in the foregoing example would be alteredcommensurately. However, the given example indicates the extremely finesubdivision of the void portion obtained in the filter of thisinvention.

The degree of the reduction in size of the macrovoids is dependent uponthe amount of radial compression which takes place between the initialroving 18 and the finished rope 21 and plug 27. Consequently, a largerdiameter roving suffers a greater reduction of the macro-voids than doesa smaller diameter roving, and in this way, the passage size can bepredetermined with reasonable accuracy. Passage size can also bepredetermined by a preselection of the diameter of the fiber in therange of between about two and about twentynine microns, for example,and by a choice of the quantity of such fibers employed.

Although the fibers need not be of uniform diameter, it has been foundthat passage regulation by radial com pression is facilitated when thefibers are of uniform diameter, but of indiscriminately varying lengthwithin the aforementioned length range. In any case, the fibers shouldbe of a fineness such as to be silky and not prickly to the tongue orskin, even when of short length. Generally speaking, the fibers shouldbe materially less in diameter than the diameter of human hair, asdescribed in Betts Patent No. 2,327,991.

In order to give the plug 27 resiliency and the whole mass integral formand proper firmness when the roving has been radially compressed in theplug-making machine to a fraction of its free diameter, I may apply abinder in liquid form to the semi-felted web fibers by means of a finemist-like spray prior to gathering the web together into the roving orstrands 13, 14, 15. The liquid may be resin dissolved in a solventvehicle or a slurry of finely-divided resin in water. The extent of thisapplication of binder approximates 15% by weight, and the binderpreferably is of the thermo-setting type, such as aphenolic-formaldehyde. The moist web is then gathered into the roving orstrands, as described.

The roving or strands, either separately or after combination into theroving, with or without prior drying, is then passed through a heatingzone where it is heated to a temperature suificient to cure or set theresin. The degree of heating employed and the length of time forexposure thereto is selected to accomplish proper curing without unduediscoloration of the binder. Each fiber is encased in a thin film ofresin, which renders it resilient. The resin coating is indicated at 33in FIG. 4 as enveloping each fiber. As an incident to the resin curing,the points of contact of adjacent fibers are secured together by thebinder. When the roving is compressed radially into the reduced diameterrope in the cone 20, the rope 21 is firm but resilient. The inherentflexibility of the resin-coated fibers enables them to flex spring-likeduring compression. It will be understood that the diameter of thefibers 31 will be increased slightly by the thickness of the coating 33.

A different but preferred mode of binding the fibers together iseffected during the plug-making operation, and that is done by addingthe dry binder, in uncured or inactive condition, either in the form ofa dry powder, staple or filaments. One convenient way of incorporatingthe thermo-responsive binder is to mix it with the fibers duringsemi-felting in the web before the latter is formed into the roving 18or roving-forming strands 13, 14, 15. Preferably, the binder in dry formis incorporated in the roving or strands either by mixing the finepowder or the staple in the web prior to its formation into the rovingor strands, or as continuous filaments in the roving or strands 13, 14,15 when the web is gathered into such roving or strands. In this way,greater uniformity of distribution of the thermo-responsive resinthroughout the eventual rope and consequent uniform distribution of thebinding points are obtained. Thus, as the semi-felted web is gatheredinto the roving or roving-forming strands, a plurality of filaments ofthermo-responsive material are fed into and thus are distributedthroughout the roving or strands. The volume of resin to fiber by weightis between about to about 25%, depending on the gauge of thethermoresponsive filaments.

Preferably, such binder staples or filaments are larger in diameter thanthe filter fibers and may be from about 2 to about 8 denier, i.e., onthe order of about 14 to about 29 microns diameter. Any suitablethermo-plastic resin, in the form of powder, staple or filament, havinga fusion point below about 300 F., the scorching temperature of thepaper wrapper 25, and above a dead storage temperature of about 150 F.and being otherwise inert as well as odorless and tasteless will servethe purpose. Examples are vinylidine chloride, vinyl copolymer,polyethylene, polystyrene, and their equivalents which are variouslyidentified by the trade names Plas-Teca, V-inyon, Polythene, Lucite,Lustron, Dynel, and the like. Alternatively, the thermo-responsiveresins may be applied in a liquid suspension or slurry and sprayed onthe web prior to gathering the web into the roving 18 or strands 13,'14, as previously described, but deferring the setting orthermoactivation of the binder until after the roving is formed into therope 21.

Assuming that the binder is of the thermo-setting type, thepaper-wrapped rope, after the seam of the paper wrapper 25 is sealed at26, is passed through a heating zone indicated at 29 in FIG. 1, whereinthe resin is heated to the curing or setting temperature to bind thefibers together in the manner described. The heating means of heatingzone 29 may be of any desired type, but in order that the heating zone29 is not inordinately long for use with modern high-speed plug-makingmachinery, a quick and penetrating heat is preferred, such as thatinduced by a high-frequency induction coil, in the field of dielectricplates, infra-red ray heat emitting coils, or the like, through, betweenor adjacent which the wrapped rope passes.

Where the binder is of the thermo-plastic type, such as vinyl chloride,vinyl chloride-acetate copolymer, methyl methacrylate or other acrylicresin and the like, the heatsoftened resin must be cooled beforesevering at 28 and to that end, the wrapped rope is cooled in a suitablecooling zone 30, which may be afforded by a blast of air throughrefrigerating coils, or the like. Although cooling is not essentialwhere thermo-setting resins are used as a binder, cooling down beforesevering at 28 is nevertheless preferred. Cooling may be renderedunnecessary by applying the resin-activating heat after therope has beensevered into the shorter lengths 27.

Whatever binder and method of activating the same are employed, thefibers are held together by the binder in the aforementioned compressed,heterogeneous arrangement, which is generally illustrated in FIG. 3,which is an enlargement of a section of FIG. 2, and in which the fibersconstituting the filter are designated 31 and the binder is designated32. It will be observed that the ratio of gross passage volume to grosssolid volume indicated by FIG. 3 is very large. I have calculated theratio to be on the order of 25 to 1 where glass fibers on the order ofabout 3 microns diameter are used, thereby indicating that the porosityof the filter volume is high so as not to impair the draw,notwithstanding the high degree of filtering efiiciency of the filter inselectively removing the larger particles from the smoke drawntherethrough.

Instead of wrapping the rope 21 in the paper 25, equivalent wrapping orconforming means such as cellophane or a sprayed coating of moltenresin, a resin slurry or solution or the like may be employed to holdthe rope 21 in its confined form after the resin envelope has beencured, set, or dried in the manner described in connection with thebinder resin, and accordingly the term wrapper as used herein and in theappended claims applies equally well to a sheet material wrapper and aplastic wrapper applied and formed in situ in the manner described.

Although a preferred embodiment of the invention has been illustratedand described herein in connection with cigarette filters, it is equallyapplicable to cigar and pipe use as Well as for gas mask and otherrespirator cartridges, being made in the proper diameter for thatpurpose. It is accordingly to be understood that the invention is notlimited to the uses described herein, but is susceptible of changes inform and detail within the scope of the appended claims.

I claim:

1. A method of making cylindrical tobacco smoke filter units, whichcomprises mixing fibers of random lengths between about .03 and about2.0 inches to form a heterogeneous mass, gathering said mass into anelongated roving having a diameter in excess of the diameter of thefinished filter unit and having macro-voids between the fibers, radiallycompressing the roving into a rope having approximately the diameter ofthe finished filter unit to reduce the macro-voids to micro-voids,wrapping the rope with sheet material, and severing the rope into filterunits.

2. A method of making cylindrical tobacco smoke filter units, whichcomprises mixing fibers having diameters between about two and abouttwenty-nine microns into a heterogeneous mass, gathering said mass intoan elongated roving having a diameter two to ten times the diameter ofthe finished filter unit and having macrovoids between said fibers,radially compressing the roving into a rope having approximately thediameter of the finished filter unit to reduce the macro-voids tomicrovoids, wrapping the rope with sheet material, and severing thewrapped rope into filter units.

3. A method of making cylindrical tobacco smoke filter units, whichcomprises mixing textile fibers of between about two and about fivedenier diameter and of random lengths in excess of .03 inch into aheterogeneous elongated roving having a diameter in excess of thediameter of the finished filter unit and having macro-voids between saidfibers, radially compressing the roving into a rope having approximatelythe diameter of the finished filter unit to reduce the macro-voids tomicro-voids, wrapping the rope with sheet material, and severing thewrapped rope into filter units.

4. A method of making cylindrical tobacco smoke filter units, whichcomprises mixing textile fibers of a substantially uniform diameterbetween about two and about five denier and of random lengths to form aheterogeneous mass, gathering said mass into an elongated roving havinga diameter in excess of the diameter of the finished filter unit andhaving macro-voids between the fibers, radially compressing the rovinginto a rope having approximately the diameter of the finished filterunit to reduce the macro-voids to micro-voids, Wrapping the rope withsheet material, and severing the wrapped rope into filter units.

5. A method of making cylindrical tobacco smoke filter units, whichcomprises mixing textile fibers of a substantially uniform diameterbetween about two and about five denier and of random lengths with otherfibers having a diameter up to about 3.0 microns to form a heterogeneousmass, gathering said mass into an elongated roving having a diameter inexcess or" the diameter of the finished filter unit and havingmacro-voids between the fibers, radially compressing the roving into arope having approximately the diameter of the finished filter unit toreduce the macro-voids to micro-voids, Wrapping the rope with sheetmaterial, and severing the wrapped rope into filter units.

References Cited in the file of this patent UNITED STATES PATENTS2,159,121 Alley May 23, 1939 2,202,839 Davidson June 4, 1940 2,221,443Davidson Nov. 12, 1940 2,230,271 Simpson Feb. 4, 1941 2,327,991 BettsAug. 31, 1943 2,357,392 Francis Sept. 5, 1944 2,476,582 Browne et a1.July 19, 1949 2,527,628 Francis Oct. 31, 1950 FOREIGN PATENTS 665,278Great Britain Ian. 23, 1952

1. A METHOD OF MAKING CYLINDRICAL TOBACCO SMOKE FILTER UNITS, WHICHCOMPRISES MIXING FIBERS OF RANDOM LENGTHS BETWEEN ABOUT .03 AND ABOUT2.0 INCHES TO FORM A HETEROGENEOUS MASS, GATHERING SAID MASS INTO ANELONGATED ROVING HAVING A DIAMETER IN EXCESS OF THE DIAMETER OF THEFINISHED FILLTER UNIT AND HAVING MACRO-VOIDS BETWEEN THE FIBRES,RADIALLY COMPRESSING THE ROVING INTO A ROPE HAVING APPROXIMATELY THEDIAMETER OF THE FINISHED FILTER UNIT TO REDUCED THE MACRO-VOIDS TOMICRO-VOIDS, WRAPPING THE ROPE WITH SHEET MATERIAL, AND SEVERING THEROPE INTO FILTER UNITS.